Subsets of 1 to 10 with a single adjacent pair
Question
Count the subsets of in which exactly one pair of elements are consecutive integers. For instance, qualifies because is its only consecutive pair.
Short answer
. Glue the consecutive pair into one block, so the set is isolated singletons plus that block, with gaps between all pieces. Placing these pieces in slots can be done in ways, and any piece may be the block, so the count is .
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Open the worked solutionLessons behind this question
- Counting and Combinatorics
- Sample Spaces, Events, and the Probability Axioms
- Conditional Probability, Total Probability, and Bayes' Rule
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